The measurement of the viscosity of complex solutions is a ubiquitous problem in biological, biophysical and biotechnological sciences. In addition, viscosity plays an important part in a wide range of technological applications that are based on fluid flow.
It is desirable to measure the viscosity of a fluid sample using high-throughput techniques using low volumes of sample. Several micro-rheological approaches have been described as alternatives to conventional viscometers and rheometers.
A common strategy for determining fluid viscosity involves monitoring the diffusion motion of tracer particles of known size. The movement of a single tracer particle may be monitored by video-microscopy (see, for example, Valentine et al. and Tseng et al.). Alternatively, the motion of tracer particles may be monitored by recording fluctuations in the average light scattering or fluorescence signal of the tracer particles (see, for example, Mason et al.; He et al.; Palmer et al.; and Goins et al.). In these approaches, the viscosity of the fluid is readily quantified from the measured apparent diffusion coefficient of the tracer particle, as understood from the Stokes-Einstein relationship between viscosity and diffusion.
In diffusion wave spectroscopy (DWS) and single particle tracking, a generalized Langevin equation of motion can be applied to correlate the time evolution of the measured mean square displacement with the storage and loss moduli of the fluid (see, for example, Tseng et al. and Mason et al.).
The present invention provides alternative methods for the determination of viscosity, such as relative viscosity.